Field of the Invention
The invention relates to a mirror drive device capable of high-speed forward and backward driving of a mirror.
Description of the Related Art
In a mirror mechanism incorporated in an image pickup apparatus, such as a digital single-lens reflex camera, a mirror enters a photographing optical path (mirror down) during finder observation to guide an object light flux to a finder, and during photographing, the mirror retracts from the photographing optical path (mirror up) to guide the object light flux to an image pickup device.
In recent years, however, the speed of forward and backward driving of the mirror has been increased by an increase in consecutive photographing speed. Further, a power amount required by the camera is increased such that the camera can perform higher-level processing at a higher speed, and it is required to reduce electric power required for the forward and backward driving of the mirror.
To this end, conventionally, there has been proposed a technique that holds a drive shaft of a mirror holder using a torsion spring, and drives the drive shaft by transmitting rotational movement of a mirror lever driven by a cam mechanism to the torsion spring via a portion that holds the torsion spring (Japanese Patent Laid-Open Publication No. H07-168280).
In Japanese Patent Laid-Open Publication No. H07-168280, when the spring pressure of the torsion spring is low, the power amount required for the forward and backward driving of the mirror is reduced. However, when the mirror lever is driven at a high speed, the mirror holder cannot follow the motion of the mirror lever, so that it is impossible to cause the mirror to advance or retract at a high speed.
On the other hand, if the spring pressure of the torsion spring is increased, the power amount required for the forward and backward driving of the mirror is increased, and force applied to the mirror holder when the mirror is held in a finder observation position is increased. This can bring about a problem that the mirror holder is deformed to distort a finder image and change a focus distance of an image viewed through the finder.